The invention relates to methods for identifying compounds that kill bacteria or inhibit bacterial growth. The invention also relates to methods for identifying compounds that can be used to treat infections (e.g., bacterial infections in organisms such as mammals).
Bacterial cell wall peptidoglycan biosynthesis is a multistep process (see FIG. 1). Although there is some variation between bacterial species, each step in the respective synthetic pathways is essential for the growth of the bacteria. Inhibition of any step can be lethal, and each step is therefore a potential target against which new antibacterial drugs are sought. Inhibitors are already known for some steps in the biosynthetic pathway; however, bacteria have developed resistance to many of these inhibitors, thus necessitating continued searching for new antibacterial agents.
One mode of defense that gram positive bacteria use to resist a certain class of antibacterial agents (i.e., the .beta.-lactams, which inhibit peptidoglycan formation) is to produce an enzyme called .beta.-lactamase. Production of .beta.-lactamase is induced in some bacterial strains by the presence of .beta.-lactams in the cell. .beta.-Lactamase reacts with .beta.-lactam drugs (e.g., penicillin or cephalosporin), rendering the drugs inactive. Certain species of gram negative bacteria such as Enterobacter (e.g., E. cloacae, E. kobei, E. agglomerans, or E. flavus) and Citrobacter freundii also produce .beta.-lactamase, in response to the build-up of cell wall degradation products, not just in the presence of .beta.-lactams per se. Because bacterial cell walls are continuously degraded and reassembled throughout the life cycle of a bacterium, the build-up of degradation products can be due to inhibition of at least one step in the peptidoglycan biosynthetic pathway.